Arc welding

ABSTRACT

According to the invention, there is provided a method for arc welding, wherein a plasma arch having a high arc energy density may be obtained without using any solid member directly restraining the flaring of the arc but by effectively utilizing two or more concentric gas streams ejected from the torch nozzle for focusing the arc.

co ma-2 01 3M 92-1973 Unlted States Patent 1 1 3 Oku et al. [451 Sept.19, 1972 [54] ARC WELDING 2,587,331 2/1952 Jordan ..2l9/l2l P [72]Inventors; T k 0 Suita; Kazushige 3,272,962 9/ 1966 Mauskapf ..2l9/ 121P Hi Ik d Yoshimitsu Mats- 2,906,858 9/1959 Morton, Jr. ..2l9/ 121 Pmoto, Toyonaka, all of Japan 3,534,388 10/1970 Ito et al. ..2l9/l2l P[73] Ass1gnee: lMltaitsuslslltlaa 1:111:32? Industrial Co., Prim?Examiner j v. Tmhe Assistant Examiner-Hugh D. Jaeger [22] Flled: Sept-1970 Attorney-Stevens, Davis, Miller & Mosher [21] Appl. No.: 68,747

[57] ABSTRACT [30] Foreign Application Priority Data According to theinvention, there is provided a method for arc welding, wherein a plasmaarch having Sept. 4, 1969 Japan ..44/7l5l9 a g are gy density y beobtained without 52 us. c1. ..219/121 P, 219/75 using any solid memberdirectly restraining the flaring 51 Int. Cl. ..B23k 9 00 of the are butby efiectively utilizing two or more [58] Field of Search ..219/121 P,75, 121 centric g stream ejected from the torch nozzle for focusing theare. a [56] References Cited 14 Claims, 3 Drawing Figures UNITED STATESPATENTS 3,575,568 4/1971 Tateno ..219/l2l P I l l 1 1 i I I 7 II I I I lH 9-. H "5:2 :11 [*1 1'1 20 ARC WELDING This invention relates to arcwelding and more particularly to improvements in the method for arewelding. More specifically, the invention is concerned with a method forarc welding base metals by establishing a stable arc with a high thermalenergy density as compared to the are produced in the prior-art TIG arcmethod.

The TIG arc method has heretofore been extensively employed in themelting and welding of metals, particularly ferroalloys such asstainless steel and non-ferrous alloys such as an aluminum alloy. Withthis method, however, the are produced provides relatively low thermalenergy per unit area of the weld zone. Therefore, the depth ofpenetration is correspondingly small. Also, for a given extent of fusionof the welds, the thermal loss is excessively high. In other words, thismethod has the disadvantages that the energy density of the arc and theoverall welding efficiency are low.

Extensive studies and research on the TIG arc method have heretoforebeen conducted with the object of overcoming the above disadvantages. Byway of example, certain improvements are disclosed in Japan patentpublication No. 7860/61. Also, there is known a method for TIG arecutting. To facilitate the understanding of the invention, some of theprior-art methods, to which the invention pertains, will now be brieflydescribed with reference to the accompanying drawing, in which:

FIGS. 1 and 2 schematically show apparatus for carrying out respectiveprior-art methods for arc welding; and

F IG. 3 shows, partly in section and partly in perspective, anembodiment of the apparatusfor carrying out the method for arc weldingin accordance with the invention.

A set-up to carry out the conventional TIG arc method is shown inFIG. 1. In the Figure, numeral 1 designates a tungsten electrode,numeral 2 a shield gas nozzle, numeral 3 a base metal, numeral 4a shieldgas film, and numeral 5 an are. As is seen from the Figure, in theconventional TIG arc method the arc 5 bridging the tungsten electrode 1and the base metal 3 is flared radially toward the base metal 3. Thus,the energy density of the arc in the weld zone is considerably reduced.

FIG. 2 shows an improvement of the aforementioned conventional method asdisclosed in the afore-said Japanese patent publication No. 7860/61. Inthe Figure, numeral 1 designates a tungsten electrode, numeral 2 an arefocusing guide member, numeral 3 a base metal, and numeral 4 an arc witha shield gas film therearound. As is seen from the Figure, in thiswelding method the arc bridging the space between the tungsten electrode1, and the base metal 3 together with the stream of the shield gas isguided through the arc focusing guide member 2 to reduce thecross-sectional arc area as compared to the naturally flaring arc. Withthis method, the density of the are energy in the weld zone may beoutstandingly increased as compared to the conventional TIG arc method,so that this xx method is extremely effective.

However, the are focusing guide member 2 shown in FIG. 2 does not focusthe are by merely confining the are together with the gas stream withinits passage of a small cross-sectional area, but it actually cools downthe arc to some extent, that is, it gives rise to the socalled thermalpinch effect, in effecting the focusing of the arc. In other words, theare focusing guide member 2 is subjected to the high temperature of thearc and absorbs the heat of the arc. Therefore, the arc focusing guidemember 2 is subject to the significant problem of heavy thermal wear inits practical use. To solve this problem, the guide member should beprovided with a cooling structure, for instance for water cooling it.With such cooling means, however, the thermal wear cannot be completelyprevented. Besides, such cooling means complicates the construction ofthe welding torch and makes handling of the torch more involved.

The aforementioned method for TIG are cutting is the one in which flowrate of the shield gas according to the TIG arc method is increased toobtain an arc having an increased thermal energy density. According tothis method, a powerful jet of arc plasma may be obtained, and thismethod has excellent effects in fusing the base metal with the powerfularc plasma to dip and spatter the fused or molten portion of the metalso as to sever the metal. However, this method cannot be adopted towelding.

An object of the invention, accordingly, is to provide a novel methodfor arc welding, which eliminates the above disadvantages in the priorart and overcomes the above non-compatibility of the prior-art method,and according to which an arc having an extremely high arc energydensity may be obtained.

According to the invention, a plasma are having a high are energydensity may be obtained without using any solid member directlyrestricting the flaring of the arc, but by effectively utilizing two ormore concentric gas streams ejected from the torch nozzle for focusingthe arc.

More specifically, according to the invention there is provided a methodfor arc welding base metals by causing a plasmic arc to bridge the spacebetween said base metals on one hand and an electrode facing said basemetals on the other hand, said plasmic are being produced through afirst gas stream surrounding said electrode and directed toward saidbase metals, a second gas stream surrounding and flowing in the samedirection as said first gas stream and, if necessary, a third gas streamsurrounding and flowing in the same direction as said second stream,said first gas stream having a sufficiently small cross-sectional areaand being constituted by a gas, for which the energy for transition intothe arc plasma is low, the velocity of flow of said first gas streambeing such that the fused or molten portion of said base metals thatresults when the arc plasma is created will not be pitted and spattered,said second gas stream satisfying at least any one of the conditionsthat for the gas constituting said second gas stream the energy fortransition into the arc plasma is high as compared to the gasconstituting said first gas stream, that the cooling effect of saidsecond gas stream. is great, and that the velocity of flow of saidsecond gas stream is high as compared to said first gas stream, and saidthird gas stream sufficiently shielding said electrode, said plasmic arcand said base metals from atmosphere, whereby the flaring of saidplasmic arc is restrained without using a solid member directlyrestraining the flaring of said plasmic arc.

This invention will now be described in conjunction with an embodimentthereof with reference to FIG. 3. Referring to the Figure, numeral 11designates an electrode 11 facing a base metal 12. Surrounding theelectrode 11 is a first gas nozzle 13, whose outlet opening facing thebase metal 12 has a sufficiently small crosssectional area. The gasejected from the first gas nozzle 13 constitutes a first gas stream 14.The energy required to create plasma are from the gas of the first gasstream 14 is relatively small. The velocity of flow of the first gasstream 14 is such that a fused or molten portion 15 of the base metal12, which results when the plasma arc is created, will not be digged andspattered.

Surrounding the first gas nozzle 13 is a second gas nozzle 16, fromwhich is ejected a second gas stream 17 surrounding and flowing in thesame direction as the first gas stream 14. The second gas stream 17satisfies at least any one of the conditions that the energy required tocreate arc plasma from its gas is high as compared to the gasconstituting the first gas stream 14, that its cooling effect is great,and that its flow rate is high as compared to the first gas stream.

Surrounding the second gas nozzle 16 is a third gas nozzle 18, fromwhich is ejected a third gas stream 19 surrounding the second gas stream17. The third gas stream 19 serves to protect or shield the are from theatmosphere, and may thus be used where it is necessary.

Numeral 20 designates an arc having a high are energy density producedby the method according to the invention. The individual gas nozzles aredisposed such that they will not be directly exposed to the are producedbetweenthe electrode 11 and the base metal 12.

The method according to the invention is based on the operationalprinciples described hereinbelow.

In the afore-described TlG arc method, the arc produced between theelectrode and the base metal flares radially. In contrast, in the methodaccording to the invention the arc is restrained from flaring throughthe combination of the first and second gas streams l4 and 17.

Because of the facts that the first gas stream 14 has a sufiicientlysmall cross-sectional area, that for its gas a low energy is requiredfor transition into plasma, and that its velocity of flow is low, thepotential gradient across the produced arc is low. As a result, the arcis confined within the zone of the first gas stream 14.

Also, because of the fact that the second gas stream 17 satisfies atleast any one of the conditions that its gas requires a high energy fortransition into plasma as compared to the gas constituting the first gasstream 14, that it has a great cooling effect, and that its velocity offlow is high as compared to the first gas stream, the second gas streamin suit is hardly capable of constituting the path for the arc, so itconfines the are within the first gas stream while cooling the arctherewithin to focus the same. Thus, if the second gas stream is at ahigh velocity of flow as compared to the first gas stream and/or has agreat cooling effect, it promotes the recombination of ion-electronpairs in the loss. Thus, the arc is rendered thinner to provide for ahigher are energy density. Also, it is rendered stable as it is confinedwithin the zone of the first gas stream. If the second gas stream is ofa gas, for which a high energy is required for transition into theplasma state as compared to the first gas stream, the transition intothe plasmic state is more difiicult in the zone of the second gas streamthan in the zone of the first gas stream, so that the second gas streampromotes the afore-said recombination effect, contributing to confinethe are within the first gas stream zone.

As is described, by providing two or more concentric gas streamsrespectively satisfying the afore-mentioned conditions throughrespective zones or passages, it is possible, by virture of the overalleffect of these gas streams, to obtain a focused arc, which has a higharc energy density and is suitable for welding, without using any arefocusing guide member directly subjected to the arc unlike the method asdisclosed in the Japanese patent publication No. 7860/61 and withoutejecting the gas stream at a high flow rate through the arc zone unlikethe prior-art TIG are cutting method.

Experiments reveal that to obtain the effects of the invention it isessential that both the first and second gas streams, as well as thethird gas stream if it is incorporated, should satisfy their respectiveconditions as mentioned above simultaneously. Otherwise, the effects ofthe invention cannot be obtained. For example, if the second gas streamalone satisfies its condition as mentioned above, no effects of theinvention will be obtained. Thus, to obtain the same effects asaccording to the invention with a method other than the method accordingto the invention, it is necessary to incorporate, for instance, themethod as disclosed in Japanese patent publication No. 7860/61. I

To put the method according to the invention into practice, the gasconstituting the first gas stream may be an inert gas or a mixture ofinert gases. The flow rate of the first gas stream is of course to bedetermined by taking the flow rate of the second gas stream intoconsideration. In practice, it is preferably below about 2 m/sec. Thecross-sectional area of the first gas stream zone should be as small aspossible. In practice, however, there is a lower limit for this area inorder to maintain it constant up to the immediate vicinity of the basemetal. It is preferably about 2 to 5 mm, though it depends upon the arccurrent.

Regarding the gas constituting the second gas stream, if a gas with ahigh energy to create the arc plasma as compared to the first gas streamis to be used, an inert gas for which the energy for the arc plasmaformation is higher (for instance helium rather than argon), or amixture of such inert gases is more suitable than a molecular gas (forinstance CO and N which, unlike an inert gas, requires a dissociationenergy, or the gas constituting the first gas stream. If a gas providing for a great cooling effect is to be selected, a gas possessing asmall molecular weight (for instance, He and H or a mixture containingsuch gas is appropriate. At any rate, it is advantageous that thevelocity of flow of the second gas stream is high as compared to thefirst gas stream. By way of example, a gaseous mixture containing A, COor H as the gas constituting the second gas stream may be used for thewelding of ferroalloys. As for the velocity of flow, it is effective tohave over about twice the velocity of flow of the first gas stream forthe second gas stream.

The third gas stream may be selected in a manner as in the selection ofthe ordinary shield gas, as it is used, if necessary, to protect theelectrode, arc and base metals from the atmosphere. It is particularlyessential if the velocity of flow of the second gas stream is high, forthe purpose of eliminating the intrusion of external air.

The gas of the gas streams, of course, should not have any undesiredeffect on the weld portion.

As has been described in the foregoing, the method for arc weldingaccording to the invention enables readily obtaining a plasma are havinga high are energy density as compared to the conventional TIG arcmethod. Also, as the apparatus involved is free from the portiondirectly subjected to the arc unlike the conventional apparatus forgenerating a plasma arc, the welding torch may be simplified inconstruction and its service life may be extended.

What is claimed is:

l. A method of welding base metals comprising the steps of producing anelectric arc between said base metal and an electrode facing said basemetal, flowing a first gas stream comprising a gas in which an electricplasma arc is producible by a relatively low energy, in a directiontoward said base metal to surround and in contact with at least the partof said electrode closest to said base metal and to surround saidelectric arc, and producing a plasma arc in said first gas stream, saidfirst gas stream having a sufficiently small transverse crosssectionalarea and velocity so that it does not dig and spatter the molten portionof said base metal when said plasma arc is produced therein, and flowinga second gas stream comprising a gas in which an electric plasma arc isproducible by a larger energy than the plasma arcing energy of the gasof said first gas stream, said second gas stream flowing in the samedirection as said first gas stream and surrounding said first gasstream, said second gas stream also constricting the electric arc withinthe flow of said first gas stream, thereby converting the electric arcto an electric plasma arc and constricting the plasma arc in a desiredrange without any solid mechanical constricting member closer to thebase metal than the tip of said electrode.

2. The method of welding base metals according to claim 1, wherein thegas comprising said second gas stream has a cooling capacity for theplasma arc which is larger than the cooling capacity of the gascomprising said first gas stream.

3. The method of welding base metals according to claim 1, wherein saidsecond gas stream has a higher velocity than that of said first gasstream.

4. The method of welding base metals according to claim 2, wherein thegas comprising said second gas stream has a higher velocity than thevelocity of said first gas stream.

5. The method of welding base metals according to claim 1, wherein saidfirst gas stream comprises argon, and said second gas stream comprisesC0 6. A method of welding base metals comprising the steps of providingan electric plasma arc between a base metal and an electrode facing saidbase metal,

flowing a first gas stream in a direction toward said base a roundingsaid electric arc and producing a plasma arc in said first gas stream,said first gas stream having a sufficiently small transversecross-sectional area and velocity so that it does not dig and spatterthe molten portion of said base metal when said plasma arc is producedtherein, and flowing a second gas stream in the same direction as saidfirst gas stream and surrounding said first gas stream, the gas of saidsecond gas stream having a cooling capacity for the plasma arc greaterthan the cooling capacity of said first gas stream, said second gasstream flowing at a sufficient velocity to constrict the plasma arewithin the flow of said first gas stream, whereby said plasma arc isconstricted in a desired range without any solid mechanical constrictingmember closer to the base metal than the tip of said electrode.

7. The method of welding base metals according to claim 6, wherein saidsecond gas stream has a velocity higher than that of said first gasstream.

8. The method of welding base metals according to claim 1, furthercomprising the step of flowing a third gas stream in the same directionof said second gas stream so that said electrode, said plasma arc, andthe molten portion of said base metal are protected from the ambientatmosphere.

9. The method of welding base metals according to claim 2, furthercomprising the step of flowing a third gas stream in the same directionof said second gas stream so that said electrode, said plasma arc, andthe molten portion of said base metal are protected from the ambientatmosphere.

It). The method of welding base metals according to claim 3, furthercomprising the step of flowing a third gas stream in the same directionof said second gas stream so that said electrode, said plasma arc, andthe molten portion of said base metal are protected from the ambientatmosphere.

11. The method of welding base metals according to claim 5, furthercomprising the step of flowing a third gas stream in the same directionof said second gas stream so that said electrode, said plasma arc, andthe molten portion of said base metal are protected from the ambientatmosphere.

12. The method of welding base metals according to claim 6, furthercomprising the step of flowing a third gas stream in the same directionof said second gas stream so that said electrode, said plasma arc, andthe molten portion of said base metal are protected from the ambientatmosphere.

13. The method of welding base metals according to claim 7, furthercomprising the step of flowing a third gas stream in the same directionof said second gas stream so that said electrode, said plasma arc, andthe molten portion of said base metal are protected from the ambientatmosphere.

14. The method of welding base metals according to claim 8, wherein saidfirst and third gas streams comprise argon, and said second gas streamcomprises CO

1. A method of welding base metals comprising the steps of producing anelectric arc between said base metal and an electrode facing said basemetal, flowing a first gas stream comprising a gas in which an electricplasma arc is producible by a relatively low energy, in a directiontoward said base metal to surround and in cOntact with at least the partof said electrode closest to said base metal and to surround saidelectric arc, and producing a plasma arc in said first gas stream, saidfirst gas stream having a sufficiently small transverse cross-sectionalarea and velocity so that it does not dig and spatter the molten portionof said base metal when said plasma arc is produced therein, and flowinga second gas stream comprising a gas in which an electric plasma arc isproducible by a larger energy than the plasma arcing energy of the gasof said first gas stream, said second gas stream flowing in the samedirection as said first gas stream and surrounding said first gasstream, said second gas stream also constricting the electric arc withinthe flow of said first gas stream, thereby converting the electric arcto an electric plasma arc and constricting the plasma arc in a desiredrange without any solid mechanical constricting member closer to thebase metal than the tip of said electrode.
 2. The method of welding basemetals according to claim 1, wherein the gas comprising said second gasstream has a cooling capacity for the plasma arc which is larger thanthe cooling capacity of the gas comprising said first gas stream.
 3. Themethod of welding base metals according to claim 1, wherein said secondgas stream has a higher velocity than that of said first gas stream. 4.The method of welding base metals according to claim 2, wherein the gascomprising said second gas stream has a higher velocity than thevelocity of said first gas stream.
 5. The method of welding base metalsaccording to claim 1, wherein said first gas stream comprises argon, andsaid second gas stream comprises CO2.
 6. A method of welding base metalscomprising the steps of providing an electric plasma arc between a basemetal and an electrode facing said base metal, flowing a first gasstream in a direction toward said base metal and surrounding and incontact with at least the part of said electrode closest to said basemetal and surrounding said electric arc and producing a plasma arc insaid first gas stream, said first gas stream having a sufficiently smalltransverse cross-sectional area and velocity so that it does not dig andspatter the molten portion of said base metal when said plasma arc isproduced therein, and flowing a second gas stream in the same directionas said first gas stream and surrounding said first gas stream, the gasof said second gas stream having a cooling capacity for the plasma arcgreater than the cooling capacity of said first gas stream, said secondgas stream flowing at a sufficient velocity to constrict the plasma arcwithin the flow of said first gas stream, whereby said plasma arc isconstricted in a desired range without any solid mechanical constrictingmember closer to the base metal than the tip of said electrode.
 7. Themethod of welding base metals according to claim 6, wherein said secondgas stream has a velocity higher than that of said first gas stream. 8.The method of welding base metals according to claim 1, furthercomprising the step of flowing a third gas stream in the same directionof said second gas stream so that said electrode, said plasma arc, andthe molten portion of said base metal are protected from the ambientatmosphere.
 9. The method of welding base metals according to claim 2,further comprising the step of flowing a third gas stream in the samedirection of said second gas stream so that said electrode, said plasmaarc, and the molten portion of said base metal are protected from theambient atmosphere.
 10. The method of welding base metals according toclaim 3, further comprising the step of flowing a third gas stream inthe same direction of said second gas stream so that said electrode,said plasma arc, and the molten portion of said base metal are protectedfrom the ambient atmosphere.
 11. The method of welding base metalsaccording to claim 5, further comprising the step of flowing a third gasstream in the same dirEction of said second gas stream so that saidelectrode, said plasma arc, and the molten portion of said base metalare protected from the ambient atmosphere.
 12. The method of weldingbase metals according to claim 6, further comprising the step of flowinga third gas stream in the same direction of said second gas stream sothat said electrode, said plasma arc, and the molten portion of saidbase metal are protected from the ambient atmosphere.
 13. The method ofwelding base metals according to claim 7, further comprising the step offlowing a third gas stream in the same direction of said second gasstream so that said electrode, said plasma arc, and the molten portionof said base metal are protected from the ambient atmosphere.
 14. Themethod of welding base metals according to claim 8, wherein said firstand third gas streams comprise argon, and said second gas streamcomprises CO2.